Circadian rhythms Flashcards
What are circadian rhythms?
Pattern of behaviour that occurs approx. every 24 hours which is set and reset by environmental light levels.
Name 2 examples of circadian rhythms.
Sleep-wake cycle and core body temp.
What are endogenous pacemakers?
Internal biological mechanisms that regulate an organism’s biological rhythms.
What are exogenous zeitgebers?
External cues/changes that help regulate an organism’s biological rhythms.
Who investigated influences on biological rhythms? (Briefly) How?
Michel Siffre. Extended period of time underground without exogenous zeitgebers.
What evidence did Siffre provide for influence of endogenous pacemakers?
Resurfaced mid-September believing it was mid-August. Free-running bio rhythm settled to 24.5 hrs. Sleep-wake cycle remained regular.
Briefly describe another study into circadian rhythms.
Ps 4 weeks in WW2 bunker (no natural light). All but 1 had circadian rhythm 24-25 hrs.
What did both studies into circadian rhythms suggest about sleep wake cycles?
It is free-running at slightly longer than 24 hours, but modified slightly due to exogenous zeitgeibers e.g. daylight hours, meal times etc.
Give another example of a circadian rhythm.
Core body temperature.
Why is core body temperature a circadian rhythm?
Lowest (36C) around 4:30am and highest (38C) around 6pm. Sleep normally occurs when temp drops. Temp rises at end of sleep to be alert when awake. Process lasts 24 hrs: circadian.
(AO3) What is a practical application of research into circadian rhythms?
Helps understand negative consequences of disrupted circadian rhythms. Night workers period of reduced concentration @6am = mistakes. Relationship between shift work and heart disease. Economic implications: make conditions better for shift workers (more healthy & productive).
(AO3) Explain why research into circadian rhythms lacks reliability.
Individual differences greatly impact bio rhythms. More recent studies variation of cycles 13-65 hours. Some people have natural preference for sleeping and waking late (Anais) or the opposite. Age differences in sleep patterns. Varies between people = lack of reliability.
(AO3) Why does research into circadian rhythms have low population validity?
Research involves small groups of Ps or single individuals. When something varies between individuals so much, a small sample is unlikely to be representative. Difficult to generalise. Suggests there may be other influences than the free-running clock and environmental influences.
(AO3) What is a weakness of the methodology used by researchers investigating circadian rhythms?
Poor control over extraneous variables. Still had access to artificial light (Siffre lamp). Was thought to not affect free-running rhythms but since proven that artificial light can reset ‘biological clocks’. Important extraneous (or confounding?) variable that reduces internal validity.
